Synthesis of Arylboronic Acid Ester

General Procedure for the Synthesis of Arylboronic acid ester from Arylboroic Acid with 2,2-Dimethyl-1,3-propanediol (5 mmol scale).

In a 50ml flask equipped with a stir-bar, arylboroic acid (5 mmol) and 2,2-dimethyl-1,3-propanediol (6 mmol) were combined. 15 mL dimethyl ether was added to the flask and the solution was stirred for 6 hours under room temperature. The dimethyl ether was then removed under vacuum to get the white solid mixture. The mixture was washed three times with water to remove the excess 2,2-dimethyl-1,3-propanediol. The product was dried at 50 ℃ under vacuum.

This method gave quantitative yield for 3 g scale.

Synthesis of Phenanthrone Derivatives from sec-Alkyl Aryl Ketones and Aryl Halides via a Palladium-Catalyzed Dual C−H Bond Activation and Enolate Cyclization - Journal of the American Chemical Society (ACS Publications)

A palladium-catalyzed chelation-assisted C−H activation of alkyl aryl ketones and their reaction with aryl iodides to afford ortho-arylated products is described. For sec-alkyl aryl ketones, the catalytic reaction proceeds further to give 10,10-dialkylphenanthrone derivatives. A possible reaction mechanism involving directed dual C−H bond activation and enolate cyclization for the formation of 10,10-dialkylphenanthrone derivatives is proposed.

Pd(II)-Catalyzed Hydroxyl-Directed C−H Activation/C−O Cyclization: Expedient Construction of Dihydrobenzofurans - Journal of the American Chemical Society (ACS Publications)

Pd(II)-Catalyzed Hydroxyl-Directed C−H Activation/C−O Cyclization: Expedient Construction of Dihydrobenzofurans - Journal of the American Chemical Society (ACS Publications)

Non-metal-catalysed C-C coupling

Non-metal-catalysed C-C coupling

Chinese chemists have successfully coupled aromatic molecules without the use of a transition metal catalyst - something that people have been trying to do for years with little success. Such cross-coupling reactions are crucial to organic synthesis and typically require expensive metals such as palladium. Efforts to find cheaper and more widely available alternatives have proved challenging.

Now, Wei Liu, from Wuhan University, and colleagues appear to have succeeded by using an organic catalyst, DMEDA (N,N'-dimethylethane-1,2-diamine) in the presence of the base potassium tert-butoxide. The team coupled unactivated benzene with a range of aryl iodides in the presence of the organic catalyst and the base.

"We have checked for contamination and excluded the involvement of trace amounts of transition metals" - Aiwen Lei, Wuhan University

The researchers suggest that the reaction proceeds via the formation of a radical, with the potassium salt initiating radical formation in the presence of DMEDA. 'In radical trap experiments the coupling was inhibited by a classical radical scavenger which suggested that radical species are involved,' says team member Aiwen Lei.

Could trace amounts of transition metal have contaminated the experiment? 'Obviously this is one of the most important factors,' says Lei. 'We have checked the contamination of trace amounts of transition metals by ICP [inductively coupled plasma atomic emission spectroscopy] and excluded the involvement of small amounts of transition metals in this transformation.' In addition, the potassium tert-butoxide used in the work was purified by sublimation to remove any contaminants.

Lei believes that the work could herald a new direction in organic synthesis. 'This is the first report of organocatalysis in carbon-carbon coupling or direct arylation between aryl halides and arenes, which could be considered as a conceptually different approach towards biaryl syntheses.'

Commenting on the work, Carsten Bolm, an organic synthesis expert from Aachen University in Germany, says, 'To be able to prepare cross-coupling products without the use of transition metals is an important scientific advance. Although at the present stage the substrate scope is by far too limited to make the process synthetically attractive, the findings illustrate that new reaction paths in direct C-H arylations are still to be discovered, and as such this work will be highly stimulating to the community.'

Characteristic IR Band Positions

Characteristic IR Band Positions

Group				Frequency Range (cm-1)
OH stretching vibrations
Free OH				3610-3645 (sharp)
Intramolecular H bonds				3450-3600 (sharp)
Intermolecular H Bonds				3200-3550 (broad)
Chelate Compounds				2500-3200 (very broad)
NH Stretching vibrations
Free NH				3300-3500
H bonded NH				3070-3350
CH Stretching vibrations
=-C-H				3280-3340
=C-H				3000-3100
C-CH3				2862-2882, 2652-2972
O-CH3				2815-2832
N-CH3 (aromatic)				2810-2820
N-CH3 (aliphatic)				2780-2805
CH2				2843-2863,2916-2936
CH				2880-2900
SH Stretching Vibrations
Free SH				2550-2600
C=-N Stretching Vibrations
Nonconjugated				2240-2260
Conjugated				2215-2240
C=-C Stretching Vibrations
C=-CH (terminal)				2100-2140
C-C=-C-C				2190-2260
C-C=-C-C=-CH				2040-2200
C=O Stretching Vibrations
Nonconjugated				1700-1900
Conjugated				1590-1750
Amides				~1650
C=C Sretching Vibrations
Nonconjugated				1620-1680
Conjugated				1585-1625
CH Bending Vibrations
CH2				1405-1465
CH3				1355-1395, 1430-1470
C-O-C Vibrations in Esters
Formates				~1175
Acetates				~1240, 1010-1040
Benzoates				~1275
C-OH Stretching Vibrations
Secondary Cyclic Alcohols				990-1060
CH out-of-plane bending vibrations    in substituted ethylenic systems
-CH=CH2				905-915, 985-995
-CH=CH-(cis)				650-750
-CH=CH-(trans)				960-970
C=CH2				885-895
Characteristic IR Absorption Frequencies of Organic Functional Groups
Functional Group		Type of Vibration	Characteristic Absorptions (cm-1)		Intensity
Alcohol
O-H		(stretch, H-bonded)	3200-3600		strong, broad
O-H		(stretch, free)	3500-3700		strong, sharp
C-O		(stretch)	1050-1150		strong
Alkane
C-H		stretch	2850-3000		strong
-C-H		bending	1350-1480		variable
Alkene
=C-H		stretch	3010-3100		medium
=C-H		bending	675-1000		strong
C=C		stretch	1620-1680		variable
Alkyl Halide
C-F		stretch	1000-1400		strong
C-Cl		stretch	600-800		strong
C-Br		stretch	500-600		strong
C-I		stretch	500		strong
Alkyne
C-H		stretch	3300		strong,sharp
		stretch	2100-2260		variable, not present in symmetrical alkynes
Amine
N-H		stretch	3300-3500		medium (primary amines have two bands; secondary have one band, often very weak)
C-N		stretch	1080-1360		medium-weak
N-H		bending	1600		medium
Aromatic
C-H		stretch	3000-3100		medium
C=C		stretch	1400-1600		medium-weak, multiple bands
Analysis of C-H out-of-plane bending can often distinguish substitution patterns
Carbonyl		Detailed Information on Carbonyl IR
C=O		stretch	1670-1820		strong
(conjugation moves absorptions to lower wave numbers)
Ether
C-O		stretch	1000-1300 (1070-1150)		strong
Nitrile
CN		stretch	2210-2260		medium
Nitro
N-O		stretch	1515-1560 & 1345-1385		strong, two bands

IR Absorption Frequencies of Functional Groups Containing a Carbonyl (C=O)
Functional Group	Type of Vibration	Characteristic Absorptions (cm-1)	Intensity
Carbonyl
C=O	stretch	1670-1820	strong
(conjugation moves absorptions to lower wave numbers)
Acid
C=O	stretch	1700-1725	strong
O-H	stretch	2500-3300	strong, very broad
C-O	stretch	1210-1320	strong
Aldehyde
C=O	stretch	1740-1720	strong
=C-H	stretch	2820-2850 & 2720-2750	medium, two peaks
Amide
C=O	stretch	1640-1690	strong
N-H	stretch	3100-3500	unsubstituted have two bands
N-H	bending	1550-1640
Anhydride
C=O	stretch	1800-1830 & 1740-1775	two bands
Ester
C=O	stretch	1735-1750	strong
C-O	stretch	1000-1300	two bands or more
Ketone
acyclic	stretch	1705-1725	strong
cyclic	stretch	3-membered - 1850 4-membered - 1780 5-membered - 1745 6-membered - 1715 7-membered - 1705	strong
,-unsaturated	stretch	1665-1685	strong
aryl ketone	stretch	1680-1700	strong

A good general reference for more detailed information on interpretation of infrared spectra (as well as other spectroscopic techniques) is Silverstein, R.M.; Bassler, G.C.; and Morrill, T.C.Spectrometric Identification of Organic Compounds. 4th ed. New York: John Wiley and Sons, 1981. QD272.S6 S55

Identification of Aromatic and Alkyl Halides

Identification of Aromatic and Alkyl Halides

1 . Introduction

 

Benzene and a large number of its alkylated derivatives are liquids. Most compounds

containing more than one aromatic ring, either fused or unfused, are solids. Aromatic hydrocarbons burn with a characteristic sooty flame; compounds that contain little oxygen and have a high carbon to hydrogen ratio (benzene is 1:1) will burn at a low temperature. A large amount of carbon is produced when such compounds are burned. Aromatic hydrocarbons give negative tests with Br2/CCl4 and basic permanganate. The simple aromatic hydrocarbons are insoluble in conc. H2SO4 (class I), however the more activated ones are soluble in H2SO4 but not H3PO4 (class N2).

 

Halogen substituents may be found alone or in combination with all other functional groups. Alkyl halides are often first indicated by a positive Beilstein Test and a sodium fusion which gives a positive result for a halogen. Alkyl and aryl halides are insoluble in conc. sulfuric acid (class I). However when another functional group is present, the solubility classification is a result of the other functional group. Often an alkyl halide can be classified by the tendency of the halogen to undergo a substitution process.

 

There are no suitable general classification tests for alkanes. Saturated hydrocarbons are best identified through ruling out other possible functional groups. Alkanes are insoluble in conc. Sulphuric acid and give a negative test for halogens.

 

2 . Test for Aromatic Hydrocarbons

 

Several Classification tests for aromatic hydrocarbons (both activated and deactivated) make use of benzene ring's ability to undergo electrophilic aromatic substitution.

 

a. Fuming Sulfuric Acid

 

Simple benzene compounds which do not dissolve in concentrated H2SO4, will dissolve in fuming sulfuric acid. Fuming sulfuric acid is a powerful ionizing and sulfonating agent. Even relatively unreactive aromatics will undergo reaction. The products are soluble in the reaction medium.

 

Azoxybenzene Test

 

Aromatic hydrocarbons derived from benzene and their halogenated derivatives will react with azoxybenzene in the presence of AlCl3 as a catalyst to give a colored diazo complex. The mechanism for the formation of this compound first involves complexation of the AlCl3 Lewis acid to the azoxy oxygentation with subsequent electrohilic addition the aromatic hyrocarbon.

 

Aromatic hydrocarbons produce a deep orange to dark red colored solution, or a colored precipitate. Polynuclear hydrocarbons such as naphthalene and anthracene give brownish colors.

 

c. CHCl3/AlCl3 Test

 

Treatment of an aromatic hydrocarbon with chloroform (CHCl3) and aluminum chloride will produce the highly colored triarylcarbonium ion in solution.

The colors produced by the triarylmethyl cation are quite characteristic of the aryl groups

present. Typical colors produced are as follows:

 

Compound	Color
Benzene	Orange to red
Aryl halides	Orange to red
Naphthalene	Blue
Biphenyl	Purple
Phenanthrene	Purple
Anthracene	Green

 

3 . Tests for Alkyl Halides

 

The classification tests for alkyl halides takes advantage of the halo substituent and its ability to be displaced. The two tests for displaceable halogen are complimentary; one works best on 3° alkyl halides, while the other works best on 1° alkyl halides. Thus, by employing both these tests one can possibly differentiate between 1°,2°, and 3° alkyl halides.

 

a. Alcoholic Silver Nitrate Test

 

The test depends on the rapid and quantitative reaction of alcoholic silver nitrate with halide ion to produce insoluble silver halide (except fluoride). Silver and other heavy metals catalyze SN1 reactions of alkyl halides by complexation with the lone-pair electrons of the halide, making the leaving group a metal halide rather than a halide ion.

 

The rate of precipitation of the silver halide depends on the leaving group, I > Br > Cl, and upon the structure of the alkyl group. Any structural factors which stabilize the electron deficient carboniumion will accelerate the reaction. We thus find the expected order of reactivity: Benzyl allyl > 3° > 2°>1° > methyl > vinyl aryl.

 

Since a halo substituent is often found in the presence of many other functional groups, several functional groups have been shown to greatly facilitate the loss of a halide in the silver nitrate test.

 

b. Sodium Iodide in Acetone

 

This test involves treating a suspected halogen bearing unknown with sodium iodide in acetone and observing the rate at which a precipitate of NaX (where X = Cl or Br) is formed. The rate of the reaction of sodium iodide in acetone with a compound containing a covalently bonded bromine or chlorine is a measure of the reactivity of the compound toward SN2 substitution. This test depends on the fact that sodium iodide is readily soluble in acetone, whereas sodium bromide and sodium chloride are not.

 

SN2 reactions are concerted and involve backside nucleophilic displacement which result in the inversion of configuration of the carbon atom ath the reaction site. As might be expected,such reactions are sensitive to steric crowding. The overall rate of such reactions forrlows the order: methyl > primary > secondary > tertiary.

 

 

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